import _00GraphFuc as gf
#判断G是否为图

V={'v1','v2','v3','v4','v5'}
E={('v1','v2'),('v1','v2'),('v2','v3'),('v3','v4'),('v2','v1'),('v1','v1')}
tv=gf.isgraph(V,E)
print(tv)
V=V-{'v2'}
tv=gf.isgraph(V,E)
print(tv)
